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B.Tech. Project Presentation

SUBMITTED BY:SUMIT JAIN2010CH10118

SUPERVISOR:PROF. A.K. GUPTA

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Designing of Reclaimed Rubber Plant

Objectives• To understand and describe all the processes involved in the plant in

detail

• To find out the chemical engineering aspects involved in the production line

• To design or model equipments involved using chemical engineering principles.

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IntroductionWhat do you mean by Reclaimed rubber?

•Reclaimed Rubber is the product resulting from the treatment of vulcanized scrap (majorly rubber tires) by the application of heat and chemical agents, followed by intense mechanical working

•It has lower molecular weight than original vulcanized scrap as well as lower tensile strength

•It has almost the original plasticity of that of virgin unvulcanised rubber, thus permitting it to be processed, compounded and vulcanized

Morton M., Rubber Technology (page 496-514)

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Need•It is estimated that 13.5 m tonnes of tires are discarded every year.

•These vulcanized rubber deposits pose an environmental danger and health hazards to their surrounding.

•Three dimensional network of vulcanized rubbers make it extremely difficult to decompose the tires.

Thus, recycling of waste vulcanized rubber articles is of extreme importance to reduce pollution as well as burden on our natural resources.

Jinwei Shi, Kuang Jian, Dongyun Ren, Hua Zou,Structure and performance of reclaimed rubber obtained by different processes

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Recycling Methods1. Direct Addition• Direct addition of pulverized waste rubber to virgin rubber leads to poor

properties because of:a. Undestroyed cross-linked structureb. Weak interfacial adhesion with matrix rubbers

2. Reclaiming Vulcanized Rubber• Reclaiming is preferable to other recycling methods in solving above

mentioned problems.

Glenn Harry D., Markiewicz Walter J.,Method of reclaiming rubber

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PropertiesReclaimed rubber is generally used as blend with the virgin rubber.

•Imparts lower viscosity; indicating higher processability of the blend

•Rapid breakdown and better mixing

•Reduced scorch time and shorter curing cycles

•Good ageing

•Lower tensile strength and abrasion resistance

•Lower elongation at break; cause of presence of reinforcing fillers

T.D. Sreeja and S. N. Kutty, Cure characteristics and Mechanical properties of Reclaimed rubber blends

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Reclaiming Process•During the process, the 3-dimensional network is broken down at the crosslink sites or in the main chain bonds

•The cross link bond scission (devulcanization) changes the vulcanizates back to its original form

•The main chain scission (depolymerisation) shortens the molecular chains causing a deterioration of mechanical properties

•The conventional rubber reclaiming process can be divided into 3 major parts• Preparation• Breakdown• Refining

Jinwei Shi, Kuang Jian, Dongyun Ren, Hua Zou,Structure and performance of reclaimed rubber obtained by different processes

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Overall Production Line

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Preparation Major steps involved in this part:

•Cracking• Corrugated rolls are used to avoid slippage at the time of bite• Major difference in the speed of two rolls

•Screening

•Separation of metallic parts• Manual separation after first screening; fine metallic parts are removed with the

help of magnetic pulley

•Mechanical Separation of rubber and fiber• Shaker table with 3 separating screens• Lighter portion-fiber; heavier portion- rubber• Continuous process with fresh scrap being added to rerun at all times.

Morton M., Rubber Technology (page 496-514)

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Refining Major steps involved in mill room operations:

•Blending• Addition of certain pigments to enhance the processability of the rubber

•First Refining • Breaker refiner, 2 roll mill similar to mixing mill produce sheet 0.012 inches • Rolls are limited to max of 36” long to avoid distortion due to pressure

developed• Different diameters and speeds of two rolls to have higher friction

•Straining

•Second Refining• Finisher, set to deliver sheet of clean reclaim 0.004-0.006 inches thick.

Morton M., Rubber Technology (page 496-514)

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Break down• The most vital and influential step is Breakdown which is also known as Devulcanization and Depolymerisation

• Vulcanized rubber scrap is usually reclaimed by these two conventional methods

a) Heater or Semi-dry processb) Digester or solution process

The temperature required for softening of rubber is generally above that required for vulcanization

Roland Fulford, Damiel Martin, El Hadi Zaddi,Process for regeneration of an elastomer from scrapGlenn Harry D., Markiewicz Walter J.,Method of reclaiming rubber

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Key Factors•Particle Size• Larger the particle size, poor heat penetration i.e. longer softening time• Finer the scrap, more uniform will be the devulcanization

•Temperature• Higher the temperature, shorter the time required (Kinetically and

thermodynamically)

•Removal of fibers• Mechanical removal• Chemical removal

Economics play a vital role in the controlling of these factors

Morton M., Rubber Technology (page 496-514)John B. Macleod, micheal E. Moir, Ronald D. Myers, Peter Nicholoson, Rubber devulcanization process

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Heater or Semi Dry Process•Scrap must be ground to smaller size than digester process

•Mechanical removal of fiber prior to the process

•Scrap is somewhat moistened about 1 parts of water per 100 parts of scrap.

•Heated with live steam under pressure in trays or pans in autoclave

•Scraps are filled in pans upto the depth of 6-8 inches with perforations in trays

•Permit steam to circulate from bottom to the top of the scrap through interior of scrap for uniform same end softness

•In the range of 200-225 psi, steam is used

•Reclaim is obtained in chunks similar to cake layers

Glenn Harry D., Markiewicz Walter J.,Method of reclaiming rubberMorton M., Rubber Technology (page 496-514)

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Digester Process•Wet process with chemical treatment of fiber.

•Scrap size around 0.35-0.25 inches thick.

•Dil. Solution of NaOH is used to hydrolyse fiber in case of natural rubber and dil. Sol. Of metallic chlorides in case of SBR.

•Reclaiming agents • Reclaiming oils ( eg. Blends of alkylbenzenes and alkyl napthenes)• Volatile oils for swelling of the rubber• Less volatile oils for plasticity of the rubber

• Reclaiming catalysts (eg. Phenol alkyl sulfides, disulfides, alkali metals etc)• Strictly a batch process• Cook is followed by washing and drying process for removal of water and

hydrolysed fiber; Small amount of moisture is kept for refining operations

Jay G. Bryson, Reclaim oil for digester process for rubber reclaimingJohn B. Macleod, micheal E. Moir, Ronald D. Myers, Peter Nicholoson, Rubber devulcanization process

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Desulfurization• Devulcanisation is done by suspending a tire crumb in a swelling solvent with the addition of an alkali metal preferably sodium leading to desulfurization reaction.

•The alkali metal cleaves mono-, di-, and polysulfidic cross linkages in the vulcanite rubber to liberate rubber polymer having a molecular weight substantially equal to that of original virgin rubber.

•Carbon black can be recovered from this technique as well.

•This reaction is carried out in the absence of oxygen.

•Typically, the sulphur content in tire rubber is about 2% by weight

•Theoretically, the molar ratio of alkali metal to sulphur is 2:1 but still because of the presence of various contaminants, ratio is generally taken as 4:1.

Macleod J.B. , Moir M.E. , Nicholson P. , Rubber devulcanization processHunt L. K., Kovalak R. R. , Devulcanization of cured rubber

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Desulfurization Reaction•The desulfurization reaction of the process is described generally as follows:

[(R)n -Sx -(R')m ]y + 2xyNa+ yH2→[(R)n -H]y +[(R')m -H]y +xyNa2S

•[(R)n -Sx -(R')m ]y represents rubber vulcanisate

•It is an exothermic reaction which is carried in the presence of hydrogen gas preferably at 1380 kPa.

•Hydrogen caps the radicals formed by the breakage of sulphur bonds.

•It is heated from ambient temperature to 250 C and is kept below 300 C to prevent unwanted depolymerisation.

•It is followed by quenching with the injection of water into the mixture.

Macleod J.B. , Moir M.E. , Nicholson P. , Rubber devulcanization processHunt L. K., Kovalak R. R. , Devulcanization of cured rubber

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Mixing Rolls•An open mill(two roll mill) consists of twin counter-rotating horizontal rolls or cylinders that facilitate mixing by providing additional mechanical work to the rubber.

•The shearing action induced by the rolls cause mixing.

•The rolls often rotate at different speeds toward each other. The ration is known as friction ratio (f) ~1 to 2 ; generally 1.2 is used in industries.

•Higher friction ratio leads to greater heat generation.

•Friction, speed and the sizes of the rolls influence the intensity of its treatment. As such, data obtained from a unit specific to that machine and cannot be applied to different one.

Morton M., Rubber Polymer TechnologyMathews G., Polymer mixing technology

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Basic Mixing Operation•Both shearing action and entrainment of material into gap is responsible for the mixing process.

•The objective of the strain caused by shearing is to mix the system as a determined statistical variation of any of the properties of a series of samples to a minimum.

•The three basic principles of the mixing theory:• Total component surface contact area should increase during mixing• The elements of the surface contact area should be evenly distributed in the

mixing mass.• Mixture components must be distributed uniformly throughout the mixing

mass.

White J.L., Coran A. Y., Polymer mixing: Technology and engineering

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Calculation of various parameters

Objective: To design and calculate parameters for a given set of conditions of the material.

Conditions:

• Batch mixing with roller diameter and roller length to be 6” and 16” with mixing time to be around 20 mins

•Density of the rubber blend – 1 kg/dm3

•Velocity of the slower rotating roll to be set at 40 rpm

•Friction ratio – 1.2

•Dynamic viscosity of the blend – 50 Pa.s

•Thickness desired of the sheet – 0.0005 m

•Friction coefficient of roller bearings- 1.2

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Batch volume loading Q=(0.0065)* D* L

Where D is the diameter of the roll & L is the roller length

• This one time volume loading is determined from experiments for each material and roll size. But preliminary calculations can be made using this correlation.

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Thrust Force•Method to evaluate thrust forces is based on the hydrodynamics of rolling.

•The behavior of a polymer material approaches that of a non-Newtonian fluid

•Assumptions made to derive design equations are:• Laminar flow in gap.• No slip between the relative motion of the walls and polymer• Gravitational and inertial forces are small compared to surface forces• Flow of material is one dimensional.

Jay G. Bryson, Reclaim oil for digester process for rubber reclaimingJohn B. Macleod, micheal E. Moir, Ronald D. Myers, Peter Nicholoson, Rubber devulcanization process

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Thrust Force Considering the system to consist of a steady plane-parallel flow of viscous fluid in the gap and applying the Navier-Stokes equations

ḍ2Vx/ḍy2 = (1/µ)*ḍP/ḍx ḍP/ḍy=0 where P= pressure. In the zone of maximum pressure (ḍP/ḍx)=0. In this zone the flow rate of polymer changes uniformly from V1 to V2.

Upon Integration Vx=(1/µ)*ḍP/ḍx*(y*y/2)+C1y+C2

Morton M., Rubber Polymer TechnologyWhite J.L., Coran A. Y., Polymer mixing: Technology and engineering

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Thrust Force Substituting the value of friction ratio f=V2/V1 and applying the boundary conditions (V at -h/2 = V1 and V at h/2 = V2) and integrating P with respect to x

(specific thrust force)P=((1+f)/2)*2.22*µV1R/h

Thrust force F= PL; L length of the roll

h min gap between rolls

R roll radius

µ apparent dynamic viscosity

Morton M., Rubber Polymer TechnologyWhite J.L., Coran A. Y., Polymer mixing: Technology and engineering

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Energy Consumption•The energy consumption in batch operations may change significantly with time because of variation in the material’s plastic properties. The resistance torque to the rotation of the rolls is made of 2 components

Torque(M)= Torque for overcoming thrust forces (Mp)+ Torque for overcoming friction(Mf)

M= FDsinA/2 + µ(F+G)D

where A is the angle of seizure and G is the gravity force on roll.

Based on the principles of plastic and elastic formation.

N=M/9700ƞ , where M in kgf.cm

Electric power of mixing roll reaches its max value only for a short time. So horsepower of the motor may be 1.5 to 2 times less than the value computed.

Morton M., Rubber Polymer TechnologyWhite J.L., Coran A. Y., Polymer mixing: Technology and engineering

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Roll Productivity Batch mixing

The productivity of batch mixing rolls depends on

q=60Q1pƞ/ť

Where◦ Q1 is volume of mixture for one time loading◦ p for mixture density(0.9-1.1 kg/dm3)◦ ƞ for efficiency(0.8-0.9)◦ ť for time cycle

Mathews G., Polymer mixing technology

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Parameters calculatedS.No Parameter Value

1 One time volume loading 0.04 dm3

2 Thrust Force 2412.37 N

3 Torque applied 882.35 Nm

4 Power consumption 1.47 kW

5 Roll productivity 0.0645 kg/hr

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Future Work So far what I have achieved is the proper understanding of the reclaimed rubber industry and the various processes and equipments involved. And with the help of understanding that I have developed I have been able to design and calculate the parameters for Mixing Rolls that is used for blending and compounding purposes in Reclaimed Rubber Industry.

I intend to design the rest of the plant as well especially extruders and devulcanisation chamber under the conditions it is utilized in the plant.